This invention relates generally to dental and skeletal implants for attaching prosthetic devices to bone tissue.
There are two requirements for achieving a secure and long-lasting implant embedded in bone tissue. The implant must be mechanically strong in order to resist the stresses to which it is subjected and it must be biologically compatible with the bone tissue in order that it may encourage bone growth around it.
Implants made of metal are attractive from the mechanical strength aspect but except for a few exceptions such as pure titanium and the titanium alloy Ti 6Al 4V, most are biologically undesirable in that they release metal ions which are harmful to living tissue. Implants made of ceramics such as single-crystal alumina do not release harmful ions and are mechanically strong but do not bond well to living tissue. Biologically-compatible ceramics such as apatite, which bond well to living tissue, lack the mechanical strength required of implants.
Because of its mechanical strength and its ease of fabrication, metal remains the material of choice for most implants. In order to enhance the growth of living bone tissue, the metal implants are coated with biologically-compatible materials. In order to minimize the inadequacies of biological bonding, the implants are often screwed into the bone tissue thereby seeking to achieve by mechanical means what can""t quite be achieved by means of biological bonding. In order to maximize the effects of bone growth to the greatest degree possible, the implant is provided with holes, recesses, and other features into which bone growth may proceed, hopefully thereby preventing the implant from loosening over time.
Unfortunately, the bone tissue often does not grow back into the interspaces between the implant and the bone tissue where it is lodged. Instead, soft tissue grows in these regions. This soft tissue contributes little to the strength of attachment between implant and the adjacent bone tissue.
The present invention is a method and apparatus for embedding an implant of a special design in a way that encourages bone tissue growth in and around the implant thereby achieving greater attachment security over longer periods of time. The method comprises the steps of forming a hole in the bone tissue at the desired site of the implant, collecting the bone fragments that result from forming the hole, crumbling the bone fragments, packing the crumbled bone fragments in the hole and in and around the implant, and installing the implant in the hole.
The method steps of forming the hole in the bone structure and collecting the bone fragments are performed with a bone-fragment collecting drill comprising a coaxial assembly of a tubular saw and a drill, the tubular saw and drill acting in concert to form the hole and deliver the resulting bone fragments to an enclosed region between the tubular saw and the drill.
The crumbling step is performed with a hand-operated crumbling device comprising a pliers-like assembly wherein the jaws are spoon shaped, the convex surface of one jaw mating with the concave surface of the other jaw when the jaws are closed. The user performs the crumbling step by placing the bone fragments in the concave lower jaw and repeatedly opening and closing the jaws to accomplish the crumbling function. The crumbled bone fragments are either retained within the spoon-shaped lower jaw or, alternatively, sieved through small openings in the lower jaw.
The implant comprises a main portion and a terminal portion. The main portion has one or more helical channels embedded in the surface of the implant for the purpose of transporting crumbled bone fragments that are placed in the bone-tissue hole prior to the installation of the implant. Transverse through holes are provided at various levels along the implant longitudinal axis to permit bone tissue growth into the implant.
The method step of packing consists of partially filling the hole with crumbled bone fragments and also packing the implant channels and holes with crumbled bone fragments.
The method step of installing the implant consists of installing the implant in the hole. Interface regions between the implant and the bone tissue become filled with the patient""s own bone tissue during the installation process thereby greatly encouraging the further growth of bone tissue in and around the implant.